Substructure, Ground Floors, Drainage and Basements

5.3Drainage below ground

This chapter gives guidance on meeting the Technical Requirements for foul, surface water and ground water drainage systems.

This chapter does not apply to the adoption of sewers under Section 104 agreement of the Water Industry Act 1991 or the Sewerage (Scotland) Act 1968. For information on standards required for adopted sewers, contact the local sewerage undertaker and other relevant authorities.


For the purposes of this chapter, the following definitions apply:

Access point Provision to access a sewer or drain for maintenance or inspection and includes any manhole, inspection chamber or rodding eye
CurtilageThe area of land around a building, or group of buildings, which is for the private use of the occupants of the buildings
FreeboardThe distance between the design water level and the top of a structure, provided as a precautionary safety measure against early system failure
GullyAssembly to receive water for discharge into a drainage system
Infiltration system Are systems that are specifically designed to promote infiltration of surface water or treated effluent into the ground. There are many different types of drainage components which can be used to facilitate infiltration. Some of these include soakaways, infiltration trenches, infiltration basins and drainage fields for use in wastewater treatment
Inspection chamber Structure with a removable cover constructed on a drain or sewer that permits the introduction of cleaning and inspection equipment from surface level, but does not provide access for personnel
Local authorityIncludes an authority acting in any relevant capacity including a Local Planning Authority (LPA), Lead Local Flood Authority (LLFA) or SuDS Approval Body (SAB).
ManholeStructure with a removable cover constructed on a drain or sewer to permit entry by personnel
Manhole top Upper part of a manhole or inspection chamber consisting of a frame and cover and/or grating
Private drain Is a drain used for the drainage of one building or any buildings or yards appurtenant to buildings
within the same curtilage
Public sewer A sewer for the time being vested in a water company in its capacity as sewerage undertaker
Rising main A sewer through which foul sewage and/or surface water is pumped
Satisfactory outfall or
effective discharge point
Point of discharge which has been specifically designed to discharge the foul sewage or surface water and for which there is a legal right to discharge. This can be another sewer or a watercourse (if there is a legal right to discharge) or an area of land or another infiltration drainage component.
Septic tankIs a form of wastewater treatment plant and refers to both traditional in-situ constructed septic tank as well as prefabricated septic tank (or small wastewater treatment systems for up to 50 PT) conforming to BS EN 12566.